The present invention relates to a reactor circulating pump system provided with a power supply apparatus for driving a coolant circulating pump of a nuclear reactor, more particularly, for preventing reactor accidents possibly occurred upon instantaneous power failure, power breakdown or reactor trip from causing.
In nuclear reactors, a system for controlling flow rate of a coolant circulated through the reactor is employed as one means for controlling a plant output power. Specifically, the flow rate control is performed by driving a reactor circulating pump by a frequency variable power supply apparatus and varying an output frequency of the power supply apparatus to change a rotational speed of the reactor circulating pump.
An M-G set (motor-generator set) having a fluid coupling variable in slippage is used as a conventional frequency variable power supply apparatus. A system block diagram of FIG. 9 shows a conventional reactor circulating pump system comprising a pump and a power supply apparatus for the same.
Referring to FIG. 9, an in-plant AC bus 1 is connected through a breaker 2 to an electric motor 4 as one of components making up the M-G set 3, the electric motor 4 being coupled to a generator 6 through a fluid coupling 5. The generator 6 is connected to a reactor circulating pump 8 through a breaker 7.
In a normal state, the reactor circulating pump 8 is operated to hold a predetermined flow rate while a signal R from the pump 8 indicating the rotational speed of the pump 8 or the flow rate of a coolant is monitored by a controller 9. However, when a signal V indicating a voltage drop due to instantaneous power failure or power breakdown on the in-plant AC bus 1, or a reactor trip signal S is input to the controller 9, the conventional system is controlled in such a manner as not to quickly reduce the voltage supplied to the reactor circulating pump 8 and hence not to cause an abrupt change in the flow rate due to a change in the rotational speed of the reactor circulating pump 8 by utilizing rotation inertial force of the M-G set 3.
The M-G set 3 as the power supply apparatus for the reactor circulating pump 8 has been problematic in having poor reliability because a response is slow and maintenance work is required for worn portions of the rotary equipment, and in limiting a reduction in size of the reactor building because a large installation space is necessary.
In view of the above matter, there is of late a tendency to employ a static voltage-variable, frequency-variable power supply apparatus comprising semiconductor devices which has a quick response and high reliability because of including no rotary portions. However, this static voltage variable, frequency-variable power supply apparatus accompanies a disadvantage of having no inertial effect unlike the conventional M-G set 3.
Accordingly, a compensating power supply apparatus is additionally needed to maintain desired operation characteristics of the reactor circulating pump 8 in the event of instantaneous power failure or power breakdown on the in-plant AC bus 1, or reactor trip. Storage batteries have heretofore been thought as being used as the compensating power supply apparatus. However, the use of storage batteries is disadvantageous in requiring an ample installation space and troublesome maintenance work such as charging the batteries.